Implement remote skill invocation components

[gabog]

The skill invocation components should allow a bot to call skills defined in another bot.

• They should be independent from a dialog class
• They should be able to to pass down an action and parameters to the skill (as part of the activity) and be able to receive a return value from the skill (in the value property of activity)
• It should be possible to wrap these components in a SkillDialog so it is integrated with other conversations.

Tracking Status

Dotnet SDK (Tracked in 2774)

• PR
• Merged

Javascript SDK (Tracked in 1327)

• PR
• Merged

Python SDK (Tracked in 348)

• PR
• Merged